This enables testing to assess more accurate loss values of fiber links. It is also
the only method that can facilitate repeatable and reliable insertion-loss values for fiber events (splices, connectors,
bends) with an optical time-domain reflectometer (OTDR).

However, EF adoption brings its own
set of challenges, namely additional complexity and thus lack of practical use in actual deployments. To meet EF standards
with most testers today (optical loss test
sets and OTDR), an external EF mode conditioner must be placed in line between
the test transmitter and the fiber under
test. In the case of insertion-loss testing,
referencing has to be performed with the
external mode conditioner as part of the
referenced testing device.

Reduction in test time for multifiber interconnects—With substantial increases of fiber counts and in the cables
interconnecting them, MPO multifiber
interconnects have become the de-facto
industry standard in high-speed data
centers. The ability to test each MPO fiber link has historically been performed
manually using fanout cables. These are
cables having simplex connections on
one end and an MPO multifiber connection at the other end.

The tester accesses each of the simplex fibers one-by-one to test each fiber
link, which means in a 12-fiber MPO environment, each fiber must wait its turn
to be connected to the test port. Manual
testing translates to times of typically 40 minutes per 12-fiber MPO link.
While this may be manageable if making a small number of tests, when testing high numbers of MPO fiber links the
time required becomes significant. For
instance, testing a rack of 48, 12-fiber
MPOs could take a total of 32 hours. 48
MPOs x 40 minutes/MPO = 1920 minutes = 32 hours.

Enabling Tier 2 testing by technicians
of any skill level—Interpreting OTDR results can be daunting even for experienced users, and it is especially challenging for those with limited training
and experience. Having the ability to
setup, test, assess, and document the results is important. Approximately 50
percent of all OTDR measurement errors are due to incorrect settings for
measurement range, wavelength, pulse
width, display resolution, and average
time; or improper trace interpretation.

The challenge has been to automate
most test configurations and simplify
the presentation of results to enable effective use by practically any technician
regardless of experience level.

Facilitating effective troubleshootingof MPO breakout cables—Simplex andduplex connections are still predomi-nantly used on transmission and receiverequipment that requires a conversionfrom MPO to individual breakout sim-plex or duplex connectors. The most com-mon method used today is to employ anMPO breakout cassette. In this setup, a“cassette” is equipped with a multifiberMPO-style connector on one side, whileon the other side of the cassette simplexconnectors are placed with individual fi-bers connecting them inside the cassettewith a predefined polarity order.

These cassettes can be problematic
due to 1) the number of connectors in
each cassette, and 2) the short length of
the fiber inside the cassette between optical connections. In order to isolate an
issue in the cassette to a specific connector, a higher-resolution OTDR with
a very short attenuation dead zone (
approximately 1 meter) is needed.

Solving challenges
individually and together

Recently some innovations have been
made to Tier 2 test equipment that address the challenges outlined above and,
by doing so, improve fiber deployments.
Please be aware that the technologies
and methods described here cannot necessarily be implemented with all OTDRs
from all manufacturers. The descriptive information that follows is based on

Shown here is a test setup using both an EF mode conditioner and a 1x12-fiber MPO
optical switch. The EF mode conditioner ensures accurate, standard-compliant launch
conditions and the optical switch reduces the time required to conduct testing.